How to calibrate dial indicators, gauges and scales

T

trainee

#1
Hello Everybody!
this is my second post here, but i have been reading this forum for a while and it has been really really helpful.
I have several questions about calibrating measurement instruments.
How do you know how often you should calibrate your scales? specially if you haven't performed any traceability or r&r study...
And second, How do you calibrate a dial indicator? I'm not even sure if I should or not calibrate them.I have never dealt with this kind of gauges before...

Thank you very much!!!!
 
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D

Don Palmer

#2
Re: Dial indicators, gauges and scales calibration

Hi Trainee, Welcome to 'The Cove'.

First of all, I'm not a calibration expert. There are members here on the forum that are though. And hopefully one of the moderators will move your post to the 'Calibrations Section' where your questions will get more notice for response.

Some generalized answers to your questions. 1st, a good rule of thumb for setting calibration cycles (when do I recertify this thing) is to follow the manufactures (mfr of the scale) instructions. Additionally, you would want to keep mindful any specific requirements called out by the O.E.M. or your engineering people. If you have no previous history about reliability/certainty of the scales, then if the scale mfr did not set a schedule requirement, annual recertification would probably suffice.

As to dial indicators, we use a certified gauge block set of standards. They are locked up and used for certifying our calibrated tools only. We maintain another gauge block set for everyday shop use.

Hope this helps a little till the experts can answer your question in more detail.

Cheers,
 

Miner

Forum Moderator
Staff member
Admin
#3
Re: Dial indicators, gauges and scales calibration

Hello Everybody!
this is my second post here, but i have been reading this forum for a while and it has been really really helpful.
I have several questions about calibrating measurement instruments.
How do you know how often you should calibrate your scales? specially if you haven't performed any traceability or r&r study...
And second, How do you calibrate a dial indicator? I'm not even sure if I should or not calibrate them.I have never dealt with this kind of gauges before...

Thank you very much!!!!
Welcome to the Cove. While this post does relate to ISO 9001, I moved your post to a more relevant forum frequented by metrology/calibration experts.

You should clarify what you mean by the term scale. Is this a scale used to measure length (e.g., six inch scale), or a scale used to weigh product?
 

BradM

Staff member
Admin
#4
Re: Dial indicators, gauges and scales calibration

Howdy! :bigwave: and Welcome!

Great thread by Don.

First, by no means am I an expert; there are experts on here, though. But, I'll give your question a shot. It is a good question, and it does come up a lot.

Here are some threads on this subject that may help you:

Weighing scales to be used at each machine on the shop floor

Calibration Frequency - Control of Monitoring and Measuring Devices - Clause 7.6

Specificity in Weigh Scale Calibration Frequencies

As far as calibration frequency, here are my suggestions:

1. You determine that the instrument shall/must be calibrated.

1. Determine any regulatory/specification requirement that you may have to comply with.

2. Determine any customer-specific requirements that have been established.

3. Say #1 applies, but 2 and 3 don't state anything specific, then you need to determine how often. Generally, the more critical the impact of the calibration failure, the shorter interval you want to keep. Calibration frequency is a trade-off, and you have to determine that. The shorter cycle the more costly. The longer the cycle, the more risk.

Also, maybe ask around with some friends in the business, vendors, suppliers, "friendly" competitors, and see what calibration frequency they have established.

Miner's question regarding scale also applies for me to the dial indicator. Don assumed (hopefully correctly) that you were referring to a depth gauge, or a caliper. Is that correct? Or, is this a temperature dial indicator, or pressure?

If you are looking at this device, and you are a bit unsure about calibrating it, it may be a wise move to find a competent calibration lab suitable for calibrating these devices. It may save you a lot of headache and trouble in the end.

However, if you would like to give some more specifics regarding the instrument, your general calibration competencies, and the like, we can probably provide some more detailed information.

Also, calibration of particular instruments have been covered extensively at the Cove. We (or if you like, experiment with the search function above) can find some threads already covering your instrument.

Look forward to seeing your re-posts!
 
T

trainee

#5
Re: Dial indicators, gauges and scales calibration

Thank you guys!!!
I'm just reading all that information you provided me.
My dial indicator is a depth gauge, a hand-held device. The scales are weight scales, but i have no problem with them so far.
Thank you very much!
Have a great day!
 
C

crendfrey

#6
Re: Dial indicators, gauges and scales calibration

Greetings and welcome Trainee:bigwave:

However, if you would like to give some more specifics regarding the instrument, your general calibration competencies, and the like, we can probably provide some more detailed information.
Brad is absolutely correct.
A little more info including the application of the devices will help us help you.
 
T

trainee

#7
Re: Dial indicators, gauges and scales calibration

I'm using a dial indicator to check thickness in the samples of my product when I perform quality checks several times a day.
Do I have to do stability and R&R studies after i calibrate them?
I know we used to do for toquimeters (force gauges) stability and traceability studies once a year, and they were calibrated once a year too.
That's the way it should be? Or can I do those studies more often?
Thank you for your help.:tg:
 
B

Benjamin28

#8
Re: Dial indicators, gauges and scales calibration

As stated in prior responses, if you have no regulatory requirements, or client requirements for calibration intervals, then it's a matter of cost vs risk in determining your cal interval. You should be cautioned, if you have no history data that establishes instrument performance you should start with a smaller calibration interval. Say you do monthly calibration for the first year, calibrations show no excessive variation, good instrument performance. You can then use these records to substantiate a change to a 3 month interval.

Gage R&R is a useful tool for determining whether the instrument you are using is suitable to the task it's performing, and what type of variation you have between users. It really isn't a required action, it's used more as a tool to evaluate your measuring systems performance.

As for your gage blocks, typically these are calibrated annually by an outside accredited laboratory.

The same will apply for your scale, and you will need master weights again calibrated by an outside lab.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#9
Re: Dial indicators, gauges and scales calibration

The best answer is to have a lab accredited to ANS/ISO/IEC 17025 calibrate all your instruments.....then use the gage blocks and weights as check items for periodic checking.....

Scales in particular can be a challenge.....after all, uncertainty components like bouyancy, local acceleration of gravity, and barometric pressure all affect scale calibration, which is why they need to be calibrated where they are actually used.....and never moved by the users.....

Hope this helps.

Hershal
 
C

crendfrey

#10
Re: Dial indicators, gauges and scales calibration

Greetings Trainee,

I think I am confused.
I have a few questions……

To what standard are you being held, assessed against, or complying with?

This makes a great deal of difference to the type of advice you receive.
Do you have 6 gages and 4 scales of 500 of each?
Do you do your own calibrations in house or send a few as masters out for comparisons, or sent them all out? What are the qualifications of whom ever is doing the calibrations?
Selecting an accredited lab may answer a lot of issues for you.

Why do a R & R after calibration when calibration should give you the performance as found and after correction (if necessary to correct) and the uncertainty of the results?

Do you just need some system of interim checks between calibrations (like GMP)

Do the operators question the performance of said devices? They use them every day, they know if something is not right (or should)

Are any of the devices legal for trade?

What do the manufacturers of your devices suggest for calibration?
Are you using said devices according to the stated manufacturer’s specifications?

I’m sorry, could go on……..just the way my mind works ……apologies.
 
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